Kalkwasser in a FW tank?

[Mako]

I've been a plant-tank nut for years, and just started keeping saltwater/reef tanks. Since kalkwasser does good at keeping pH up, and best of all, precipitates phosphates, wouldn't it be a good idea to use kalk in a hardwater FW tank, like a rift cichlid or livebearer tank? The stuff is cheap ($2 a pound sold as pickling lime at the grocery) and easy to use, so long as you don't pickle your fish by adding it too quickly.

Biochemists out there, your thoughts?

Mako

 

[mogurnda]

Not a biochemist, but a physiologist. Anyway, I use kalk for my Tanganyikans. Works fine, although I am not as compulsive about montioring their Ca/alkalinity as I am with the reef tank.

 

[Mako]

Yeah, I wouldn't sweat the ca levels either. Does the kalk keep PO4 precipitated out in freshwater? I'm not sure how the extremely lower levels of magnesium (compared to seawater) would affect it. I can imagine that PO4 would build up like a chowder in a heavily stocked/fed cichlid tank, especially if there are no plants.

 

[mogurnda]

If I were to hazard a guess, I'd say kalk wouldn't precipitate much PO4 in a cichlid tank. In a SW tank, the Ca levels are close to saturation, so the addition of kalk gives a local concentration that would precipitate PO4. The Ca levels are a lot lower in FW. It should be indifferent to Mg, I think.

 

[Mako]

I chatted with a chemistry professor that I go to church with about PO4 and kalk (we had to have something to do while waiting for our cue in the Christmas play). He said that pretty much any hydroxide would precipitate PO4 out of solution. Potassium hydroxide would really do wonders, but of course it would turn the entire biomass of the tank into a primordial sludge (ie, a bad bad idea). Calcium hydroxide is about as safe as you can get for an aquarium